Field of the Invention
Aspects of the present disclosure relate to a post processing apparatus and an image forming apparatus that perform post processing such as a shifting process on a recording material on which an image is formed.
Description of the Related Art
A post processing apparatus has the functions of performing post processing such as a shifting process on sheets of paper conveyed from an image forming apparatus and placed on a processing tray and discharging a batch of the sheets having undergone the post processing to a placement tray.
In some cases, the sheets conveyed to the post processing apparatus are curled. When the sheets are curled, the post processing apparatus is not necessarily able to accurately perform the post processing. Consequently, placement suitability of the sheets is degraded. In order to address this, a variety of methods have been proposed for correcting such curl of sheets.
For example, Japanese Patent Laid-Open No. 60-52459 describes a technique for correcting curl of sheets with a dedicated decurler mechanism that corrects curl of sheets by bringing decurl rollers into pressure contact with sheets. Japanese Patent Laid-Open No. 2006-089197 describes a technique for correcting curl of sheets by moving upward a placement tray on which a batch of sheets are placed so as to bring the upper surface of the batch of sheets into contact with a top plate.
Here, with the technique described in Japanese Patent Laid-Open No. 60-52459 in which curl is corrected by the decurl rollers, the structure of a device becomes complex because of the dedicated decurler mechanism. This increases the cost and the size of the device. With the technique described in Japanese Patent Laid-Open No. 2006-089197, since the placement tray is moved close to the top plate, new sheets cannot be received during decurling. This degrades productivity.